Mains Trip

[bargeboy]

Hiya, just thought I'd ask on this forum to see wether I'm going about this the right way before I have to possibly call in an electrcian. Firstly let me explain the problem. I'm hooked up to 240v shore line and have a RCB onthe boat which has two circuit breakers in it. Now somehow a fault has developed that is causing the shore post trip to trip out, which as you can imagine, is annoying for my neighbours.

Now i've checked all plug sockets, the extension cable to the shoreline, turned everything off, bypassed the RCB on the boat (something i was hesitant to do) and the problem still occured. This led me to believe then that there was a fault somewhere on one of the ringmains. What I did next is to plug it all back in so that it was running through the RCB again and see wether i could work out what was causing the trip via the two circuit breakers. One seems to be for the plug sockets, and one seems to be for the overhead 240v lights. with the circuit breaker for the lights turned off, i havent had any problems with annoying trips so that has led me to believe that the problem is with the light circuit.

I've figured that the next step is to check all the light fittings and make sure there are no loose wires, i've had a quick look and can't see any loose wires anywhere, its probbaly worth mentioning that the trips have occured when there are no lights switched on. So now i have started to disconnect each light fitting, making sure each one is insulated with electrical tape to avoid any nasty suprises and that they cant touch anything metal or each other. I havent done them all yet and the problem is still occuring, but i assume once all the lights are "disconnected" then that would just leave wiring with no circuit and if the problem still persisits, then somehow a fault has devloped in the wiring behind the actual boat panelling (though i cant see how this can happen) i think if i get to this stage I will have to call in an electrician in as its beyond my level of knowledge but could there be any other possible causes?

One thing i should mention is that i have a flouresecent light in the bathroom and i have heard they can be a bit twitchy sometimes tho i have removed both the tube and the choke and the trip still happened. as I said, with the lighting circuit switched off then i havent had any problems with shoreline trips and the boat RCB still works when "test" is pressed. any suggestions would be much appreciated, thanx.

[Chris Pink]

Can't find a fault in your fault finding procedure, sounds like you are to the point where it is between the lighting circuit isolator and the lights themselves, if they are on a ring then it is pretty tricky to trace as there are no more options for isolating any part of the circuit.

 

I would suggest removing each light switch in turn as the next step. But disconnect the flourescent completely as the last part of checking the fittings, there may be a fault between the wire coming in and the casing. Look for places where wiring goes through bulkheads. An RCD tripping mains fault is a mechanical fault normally and mechanical damage is what you are looking for.

 

Does the trip go off instantly? or intermittently?

 

Chocolate terminal block is a good alternative to tape for holding the wires safe when fittings are removed.

[bargeboy]

thanx for the feedback, it seems to be an intermittent fault which makes it all the more frustrating, what seems to happen is that i can leave it for maybe a day or two no problem, then it will trip, then it will keep tripping every ten mins or so until eventually it trips instantly. as soon as the light circuit is inactive i have no problems. i'm hoping that its just a cases of taking out all the lights, then seeing what happens as the wiring itself is behind panels. i have a feeling its got something to do with the flouresecent light fitting, but can't see any visible signs, i guess i'll know for sure once i've disconnected it! one other thing, when i plugged the boat directly into the shore post via a cable which bypassed the RCB, the trip still occured so that should rule out any fault with the isolator?

Edited January 8, 2008 by bargeboy

[Lee J]

Hi

 

Is the fault occuring at a particular time of day? Is the boat dry, or could it be down to condensation?

 

Lee

[Keeping Up]

Can't find a fault in your fault finding procedure, sounds like you are to the point where it is between the lighting circuit isolator and the lights themselves, if they are on a ring then it is pretty tricky to trace as there are no more options for isolating any part of the circuit.

I agree with Chris, you're setting about it in the right way. It would be unusual for the lights to be on a ring - but if they are you could just temporarily disconnect one end of the ring while you fault-find. Without knowing how it's all connected up, it's difficult to make any more positive suggestions. Fluoresent lights are favourites, as you already suspect. One thing to check, is that the switches are always switching the live supply rather than the neutral; it's perfectly possible to switch a light off from the neutral side, if it has been wired incorrectly, then when it is switched off there is still 240v being fed into it relative to earth so that a fault (eg a leaky choke, or a dead spider in the terminal block) could still trip the RCD. Also of course it would be dangerous to work on because you'd assume it wasn't live when it was switched off!

[Tommo]

Now somehow a fault has developed that is causing the shore post trip to trip out, which as you can imagine, is annoying for my neighbours.

 

You say it is annoying for your neighbour, is their supply is through the same RCD, if so how do you know it is your boat causing the fault, does the RCD on your boat trip at the same time?

 

Ian

[Chris Pink]

hmm intermittent is the nadir of faults. I agree, try with the flourescent completely removed. Where each fitting is spurred off it should be possible to break the line, if it's not a ring which i guess would be overkill on a boat.

 

I can feel a diagram coming on but I'll wait and see if you know what i mean. Do you have house type switches? or on the light fittings?

[tosher]

I understood that lighting circuits do not go through the RCD on domestic systems, only socket outlets use the RCD. That is certainly the case at home but my house was wired 10 years ago, things may have changed now.

[DHutch]

Often, both the ring main and lighting circuits feed from the same 'master switch' incorporating a rcd device. Certainly this is the case for both our house and boat, both of which are 15-20years old. Although not the case in this house (newer student accomdation). Where there is a break in the bus bar half way along. With a second master switch for the lighting, which does not contain an rcd.

 

GooD luck with your fault finding!

 

 

Daniel

[chris w]

The RCD will trip if a current greater than 30mA flows between live and earth I suspect that the problem is caused by moisture on one of the light holders, terminal blocks or switches. Even a tad of moisture where the impedance is less than 8Kohms will trip the RCD.

 

Check any areas near to mushroom vents etc where dampness might ingress. Is the tripping more prevalent when the weather is bad (although less easy to check that at this time of year)?

 

Chris

[ChrisPy]

Am I right in thinking that there is something wrong with the design and balance of the protection system if the shore pillar trips out before the boat's own CB ?

 

I have a similar problem in Bristol Marina. Every two months when I arrive, I find the pillar CB has tripped. I isolate the shore lead feeding another boat (that is also on the hard but never seems to be occupied) and the pillar is fine.

[Gary Peacock]

Often, both the ring main and lighting circuits feed from the same 'master switch' incorporating a rcd device. Certainly this is the case for both our house and boat, both of which are 15-20years old. Although not the case in this house (newer student accomdation). Where there is a break in the bus bar half way along. With a second master switch for the lighting, which does not contain an rcd.

 

GooD luck with your fault finding!

Daniel

 

Most modern domestic installations use a split load consumer unit where normally only appliance related circuits (sockets etc) are protected by a 30mA RCD in the past it was common to protect the whole installation with a 100mA RCD.

[bargeboy]

thanx for the replies extremely helpful, its given me some food for thought! one of the light switches is a normal house type one, the others are on strings that you pull, i've checked the wiring on the house type one and it seems fine. as for the bollard tripping, it doesnt when the lighting circuit is turned off, but as someone pointed out, surely it should be tripping the isolator switch on the boat before the one on the bollard? weather could have a part to play with condensation etc, its just a pain as i've no real way of telling until i have disconnected all the lights themselves. once i've done that whats the next step? check the switchs? i'm a bit hesitant at messing around too much as i'm not an electrician and feel if i get to the checking switch stage its time to call in someone who knows. i still think its that flouro tho!

[Chris Pink]

. i still think its that flouro tho!

 

Yep, have it out and then see. I reckon it is the most likely unless there is obvious moisture or physical damage.

 

If everything seems fine after then put all the rest back together first before the flourescent fitting.

 

Probably also a good idea to reinstate each light after testing, except, of course, if you have more than one fault.

 

 

The reason i asked about switches is that you will have a supply cable running down the boat which is split for each light and if you can find the place it splits then you can isolate each light/switch pair.

 

edited to say: don't worry about safety as long as you disconnect the supply (unplug it!) before each investigation you will be totally safe.

Edited January 9, 2008 by Chris Pink

[bargeboy]

yes this is the intention, once i have all the lights out, i shall see what happens, fingers crossed it shouldnt trip, if it does then its going to be a headache as it must be a fault with the wiring behind the panels. assuming that nothing trips once all the lights are disconnected (think positive here!no pun intended) i'm hoping it will simply be case of reconnecting them all up one by one until i can isolate the offending light.

 

cheers for the supply cable info btw, i assume this will be behind the ceiling panelling so this could be a first port of call for an electrician should i have to get to this stage, as its probably easier for me to unwire lights than start removing panelling etc

[Chris Pink]

cheers for the supply cable info btw, i assume this will be behind the ceiling panelling so this could be a first port of call for an electrician should i have to get to this stage, as its probably easier for me to unwire lights than start removing panelling etc

 

Maybe not, if the run is put in properly then it should be possible to disconnect each fitting/switch on the main supply cable simply by disconnecting the live at each spur.

 

I don't know your boat (obviously) but the above assumes you have removable panelling (trunking) for the wiring. If not maybe you should consider this as there are few things more difficult to fix in a boat than wiring just laid loose behind the main ceiling or wall panelling.

 

As far as I know mains wiring has to be in conduit or trunking on it's own for the BSS not laid with other cables.

Edited January 9, 2008 by Chris Pink

[ChrisPy]

As far as I know mains wiring has to be in conduit or trunking on it's own for the BSS not laid with other cables.

ISO 13297 says:

11.3 An a.c. circuit shall not be contained in the same wiring system as a d.c. circuit, unless one of the following

methods of separation is used.

a ) For a multicore cable or cord, the cores of the a.c. circuit are separated from the cores of the d.c. circuit by an

earthed metal screen of equivalent current-carrying capacity to that of the largest core of the a.c. circuit.

b ) The cables are insulated for their system voltage and installed in a separate compartment of a cable ducting or

trunking system.

c ) The cables are installed on a tray or ladder where physical separation is provided by a partition.

d ) A separate conduit, sheathing or trunking system is used.

e ) The a.c and d.c. conductors are fixed directly to a surface and separated by at least 100 mm.

11.12 Conductors which may be exposed to physical damage shall be protected by sheaths, conduits or other

equivalent means. Conductors passing through bulkheads or structural members shall be protected against

insulation damage by chafing.

 

hope that helps

Edited January 9, 2008 by chris polley

[Big Steve]

Try and borrow a mega and test each circuit with that, it'll show up most such faults. Make sure both ends of the circuit are isolated before meggering it. You haven't fitted any new built in stuff recently have you? Once had a problem with a nail through the insulation, only making contact occasionally.

 

 

 

 

 

 

 

 

 

Edit to add info

Edited January 9, 2008 by Big Steve

[Dave-Shrop]

Marine bollard socket outlets should have an RCD rated at 30ma and with time delay (100ms) to allow boat RCD to trip if fault is in boat. These are very often not fitted and therefore inconvince to everyone.

[Chris Pink]

Marine bollard socket outlets should have an RCD rated at 30ma and with time delay (100ms) to allow boat RCD to trip if fault is in boat. These are very often not fitted and therefore inconvince to everyone.

 

Never had the luxury of a powered bollard, but isn't 100ms enough to cause a serious shock?

[chris w]

Never had the luxury of a powered bollard, but isn't 100ms enough to cause a serious shock?

 

Even the standard 30mS can cause a serious shock. The heart can go into fibrillation at as low as 5mA for 5mS. The latter figures are what US RCDs use.

 

Chris

[shugie]

Without seeing the circuits it's always a guess, but the RCD in the bollard might already be carrying a slight fault current from another boat, say 5mA of the 30mA, so it's "nearer" its trip point than the one on the boat, when the earth fault occurs it reaches the trip current very, very slightly before the boat one, but due to the mechanical nature of the trip both RCDs will disconnect at almost the same time, certainly on the same half-cycle.

 

RCDs will detect not just live-earth faults, but also neutral-earth faults, so you need to check both sides. An insulation tester aka "megger" is indeed the best way of checking wiring, but don't connect it to a fluorescent light fitting, or anything with electronics in it, the test voltage is high enough to damage things. It might be worth testing the RCD is operating properly, a qualified electrician will have a tester to do this.

 

Apart from cable problems, such as the traditional nail banged carelessly into the wall, the most common cause of tripping is an appliance with water in (kettle or washing machine), but an intermittent neutral-earth fault in a fluorescent fitting can happen with a metal fitting can occur when the light is still apparently functioning. Live-earth faults are usually more obvious. But a complete disconnection of the neutral and live from the fluorescent should sort you out one way or the other.